DESCRIPTION Amyloid is a generic term that encompasses a group of disorders in which extracellular hyaline material deposits in tissue that has characteristic tinctorial properties and a fibrillar structure. Fibrils are intimately associated with other constituents, notably including P-component, proteoglycans, and certain apolipoproteins, several of which also circulate in blood and other body fluids, some of which may be important in explaining amyloid deposition in specific organs or anatomic sites in tissue, and some of which have been reported to bind amyloid fibrils, their subunit proteins, prevent fibril formation, or affect the morphology of the fibril in vitro. Forms with a predilection for the central nervous system that may manifest prominent cerebrovascular amyloidosis include the prion diseases, certain hereditary stroke-like syndromes due to cystatin C or Alzheimer's disease (AD) amyloid beta protein (Ab) deposition, and Ab deposition in AD and related disorders. Three possible origins for Ab accumulation in the cerebrovasculature include: (a) local synthesis and/or processing of AD b-amyloid precursor protein (bPP) to amyloidogenic fragments by any one, or potentially several cell types, including neurons, glial, smooth muscle or endothelial cells, and/or accumulation of soluble forms of Ab (sAb) from b) cerebrospinal fluid (CSF), possibly via the perivascular Virchow-Robin spaces, or (c) through uptake from the vascular space by specific transport mechanisms at the level of the blood-brain barrier (BBB). sAb are normal metabolites of bPP variably produced by different cell types, some forms of which appear to remain soluble in biological fluids by virtue of their low concentrations, and due to binding of cofactors, notably including apolipoproteins E and J. The purpose of this proposal is to define pathogenic mechanisms that result in the localization of Ab at the level of the BBB. To this end, (1) we will study the isoforms and metabolism of bPP in an in vitro model in which rat brain capillary endothelial cells are induced to adopt the configuration of the BBB by coculture with glial cells, and utilize this system to study (2) uptake of radiolabeled Ab peptides, either alone, complexed with specific apolipoproteins, or incorporated into high and very low density lipoproteins. Differential results obtained will then be corroborated by in vivo studies in the intact rat that quantitate (3) CSF flux and distribution of radiolabeled Ab peptides solubilized in CSF injected into the lateral ventricle, and (4) uptake from the blood following intravenous administration of radiolabeled sAb into the awake animal; both sets of investigations will be interpreted in relation to previous studies that have utilized 14C-sucrose, and the kinetic models that have been derived from these experiments. Basic hypotheses to be tested are that cerebrovascular deposition results from abnormalities in bPP processing in the cerebral microvasculature, or is a consequence of accumulation of sAb that originates from the vascular space of cerebrospinal fluid.